Vapor generator furnace wall deslagger



Aug. 30, 1966 E. KocHEY. JR 3,269,365

VAPOR GENERATOR FURNACE WALL DESLAGGER Filed oct. 2o, 1964 F-'ICLI 5 F- ICLE /Mw Y United States Patent O 3,269,365, VAIR GENERATR FURNACE WALL DESLAGGER Edward 1L. Kochey, fr., Eolebroolr, Conn., assigner to Combustion Engineering, Inc., `Windsor, Sonn., a corporation of Delaware Filed Det. 20, i964, Ser. No. 405,165 3 Claims. (Cl. 122392) My invention relates to furnace wall deslagging and in particular to an apparatus for removing molten slag from tube lined furnace walls of vapor generators.

When an ash bearing fuel is burned in the furnace of a vapor generator a portion of the ash particles in the fuel deposit on the furnace wall tubes. This ash tends to build up on these walls forming a layer of ash and slag. This layer insulates the furnace walls, which disturbs the balance of heat absorption throughout the unit and also has a detrimental effect on the efficiency of the vapor generator.

Throughout the furnace the metal temperature of the wall tubing is much lower than any known ash softening temperature and consequently the ash adjacent to the tube surface must be solid. Conversely, the gas temperatures within the furnace generally exceed the ash softening temperature and the temperatures within the burner zone of an ordinary vapor generator always exceed the ash softening temperature. While the face of the slag layer which is adjacent the tubing approaches the temperature of the furnace wall tubing, the other face of the slag layer which is adjacent the furnace cavity approaches the gas temperature. Therefore, running slag can be anticipated throughout the furnace and particularly in the burner zone where there tends to be a very high heat absorption rate in the furnace wall tubing.

The method by which this ash layer forms should also be considered. The ash particles as they strike the wall surface are in a molten state and freeze as soon as they strike the walls. This continues until there is an ash buildup comprised of lightly bonded ash particles. As this becomes thicker the temperature of the outer layer increases so that the new ash particles impinging thereon are cooled less slowly and ltend to form a sintered `or vitriiied layer. As additional ash collects on the surface the surface temperature becomes high enough to permit the ash to run in the form of slag. Since most coal ash is a mechanical mixture of many compounds, the fluid ternperature of the ash is not well dened and the wall deposit exists as a layer ranging from loosely bonded ash at the tube surface through the vitrified layer of solid ash, and then through a range of viscous semi-fluid to fluid slag on the outer surface which is immediately adjacent to the furnace cavity.

Where high heat absorption rates exist, particularly in the burner zone, there is a great tendency for the formation of this vitriiied layer along with the fluid outer layer. This is so because at the high heat absorption rate the outer surface of the slag reaches the fluid temperature with a relatively thin insulating layer of ash.

Conventionally the ash layer on the furnace walls is removed periodically by conventional well known wall type soot blowers such as illustrated in U.S. Patent No. 2,662,241. These soot blowers operate by inserting a nozzle within the wall so that it blows from a position l1/2 to 2 inches on the furnace side of the crown of the furnace wall tube, and in a direction almost parallel to the furnace wall. The jet of cleaning medium tends to blow against and across the slag layer to remove the slag.

A soot blower of this type is very effective on the loosely bonded ash particles which comprise the earliest formation in the burner zone and in lower heat absorption zones comprise the total formation. However when the rice vitriiied layer forms, the efficiency of these soot blowers decreases. If the soot blower is able to penetrate the vitritied layer, it may then operate on the edge of the remaining slag layer so that it is peeled back by the action of the jet which works on the remaining edge `of the existing slag layer. The nozzle so inserted is rotated throughout 360 degrees to effect cleaning of the general furnace wall area.

According to my invention an apparatus is provided wherein a gaseous cleaning medium is introduced through a section of a furnace wall in a direction perpendicular to the wall, with the introduction being spread through a substantial area whereby the slag will permit the viscous semi-fluid slag to contain the pressure while it expands ballooning from the wall thus placing a force on the slag perpendicular to the furnace wall so that the dry layer next to the tube is put under tension permitting it to rupture and separate from the wall.

It is an `object of this invention to provide improved cleaning of slag from the furnace wall tubes which is particularly useful in a high heat absorption zone where a vitrified slag layer is formed.

It is a further object to provide an effective furnace wall ideslagger which has no moving parts that need be subjected to high furnace temperatures.

It is a further object to provide a furnace wall deslagger which may be inserted in a furnace at: the burner zone without a requirement for extensive outside fittings in that area whereby interference with air ducts and burner piping can be avoided.

It is a further object to provide a furnace wall deslagger which may be placed on the burner zone of a furnace without interfering with burner operation.

It is a further object of this invention to provide a furnace wall deslagger which may be made gas-tight since there is no relative movement between the furnace wall deslagger and the furnace wall structure.

Other and further objects of the invention will become apparent to those skilled in the art as the description proceeds.

With the aforementioned objects in view, the invention comprises an arrangement, construction and combination of the elements of the inventive organization in such a manner as to attain the results desired, as hereinafter more particularly set forth in the following detailed description of an illustrative embodiment, said embodiment being shown by the accompanying drawing wherein:

FIGURE l is a side elevation of a typical vapor generator showing a grouping of furnace wall deslaggers in a section of the furnace where they are particularly useful;

FIGURE 2 is a sectional side elevation through the furnace wall showing a detail of the furnace wall deslagger;

FIGURE 3 is -a sectional plan View through the furnace wall illustrating the furnace wall deslagger;

FIGURE 4 is 'an enlarged detail of a portion of FIG- URE 3; and

FIGURE 5 is an enlarged sectional plan view through a section of a furnace wall similar to FIGURE 4, but showing application of my invention to a web wall construction furnace.

In the illustration of FIGURE 1 the walls 2 of the furnace 3 `are lined with furnace wall tubes 4. These tubes convey water to be heated from the lower headers 5 and 6 to the upper headers 7 and 8 from which steam is released land conveyed through additional steam heating surfaces (not shown). Coal is introduced through burners 9 with combustion occurring in the Afurnace 3 and the gas passing out to exhaust through the flue 10.

Located in the furnace wall in the upper portion of the burner zone are a plurality of furnace wall desliaggers at each location I2. Although deslaggers of this .El type may be located 4anywhere in the furnace, they are particularly useful in this area of maximum heat absorption rate.

FIGURES 2, 3 and 4 show these deslaggers in detail. The furnace wall is of the so-called tangent tube construction where the tubes are not actually tangent but have about 1/16 inch space between them. Such a construction is normal on tangent Wall construction to allow for various tolerances and to give us some flexibility in fitup. The furnace wall tubes are backed up with a layer of insulation 13 which is, in turn, backed up with a metal outer casing 14.

Behind the furnace tubes and inside the insulation is a pressure chamber 1S. This chamber is enclosed in the bottom with a scalloped bar which is welded to the tubes 4 'and is enclosed on the top with scalloped bar which is also welded to the tubes. Air inlet pipe 19 is attached to the upper scalloped bar so that air may be introduced into the pressure chamber 15. Side plates 20 are vertically arranged and welded to a furnace wall tube 4 which is at the outer extremities of the pressure chamber. The enclosure is completed by the backing plate 22 which is Ireinforced horizontally with stiffening bars 23 and reinforced vertically with stiffening bars 24. These stiffeners make it possible to contain a reasonable pressure inside chamber 1S without excessive deflection of the backing plate and consequent damage to the inside or outer casing.

During operation of the unit, ash from the fuel collects on the furnace walls forming la layer of 'loosely bonded ash particles 30, a layer of vitrified ash 31 and a layer of molten slag 32. This slag starts building up on some portions of the various tubes and gradually increases until a generally contiguous layer is formed in the area of the deslagger in a particular section of the furnace Wall. After such a layer is formed and when it is desired to deslag that particular area, valve 27 is operated to introduce air through the inlet pipe I9 into the pressure chamber 15. This `air passes into the furnace through the many small spaces intermediate the furnace tubes 4. A relatively low velocity occurs as the air passes between the tubes because of the relatively large fiow tarea which exists. The flow area is available between each adjacent tube throughout the height of the pressure chamber 15. This air as it passes -through the tubes exerts la generally uniform force on the underside of the slag layer which is perpendicular to the wall. This tends to force the entire slag accumulation off from the furnace wall with the viscous layer acting t-o seal the Iair under the slag layer. The slag thus 'expands ballooning out from the wall which `removes not only the slag which is directly in front of the pressure chamber l but also slag on either side above and below the pressure chamber. As the slag balloons out the air underneath the slag layer expands underneath the slag layer exerting the same force perpendicular to the furnace walls in the adjacent areas.

It is important that the air ow perpendicular to the wall be `spread out over a relatively large area in order for this deslagger to be effective. Introduction of lair perpendicular to a wall with significant velocity will cause the air jet to break through the slag layer locally and will only break a small hole in the slag. A high velocity flow will not be effective to spread the air throughout a relatively large :area underneath the slag layer so that the air would exert a force satisfactory to clean a section of the furnace wall.

The operation of such a system should be detained until a generally contiguous slag layer is formed on the walls of the furnace. This is required since the system operates on the principle that the slag layer generally contains the air which is introduced underneath it for a sufficient length of time to dislodge the slag layer from the wall. Random holes in the slag layer will not interfere with the operation since the air confined behind the slag layer will not escape through these holes at sufficient rate to destroy the eflicacy of the deslagger.

FIGURE 5 illustrates a similar type deslagger as yapplied to a furnace of the fin-tube construction. Here the furnace tubes 4 have fins 28 Welded intermediate adjacent tubes, these fins being about 1A inch wide and 1A inch thick while running the entire length of the tubes. In the illustration of FIGURE 5 fins 2S have slots 2 cut through them throughout the height of the pressure chamber 15. These slots are about V16 inch wide and permit the air to flow between the tubes in a manner similar to that discussed in relation to the tangent tube construction. Insofa-r :as the operation of the deslagger is concerned these fins may be removed entirely throughout the location of the pressure charnber 15. The slag will not pass through into the chamber due to the cooling action of the tubes which will freeze the slag as it attempts to iiow through. However, with large openings between the tubes radiation from the furnace will tend to heat the backing plate 22 which may 'lead to high temperature corrosion. Inasmuch as it is very difficult to replace the backing plate, and furthermore deterioration -of the backing plate would put Iair pressure on the insulation :and outer casing, it is recommended that the space between tubes be limited to avoid excessive Kradiation passing therethrough. This of course will vary depending on the lfurnace conditions to which the deslagger is exposed.

All parts of the furnace deslagger system which are exposed to the hot furnace gases are fixed. We therefore have no problem with maintenance of moving parts which are subjected to such intense heat, the only moving part being the valve which regulates the flow of air and which is located well outside the furnace. These fixed parts which comprise the deslagger are also -free from high temperature corrosion problems since they are shielded from furnace radiation.

Since no equipment is required in the area of the deslagger to remove a nozzle or operate it in any manner, no outside fittings are required in this zone. The only requirement is the air supply pipe which must run up to the manifold. These deslaggers are therefore particularly well adapted to the construction of la vapor generator in a burner zone where there is often considerable interference problems with burner piping in the windbox.

Also due to the fact that .there are no moving parts in the deslagger it may conveniently be welded so as to form a gas-tight seal. The sealing boxes and aspirators which are required to have a retractable type soot blower are not required making this deslagger particularly useful for use on pressurized furnaces.

The air from this deslagger is introduced into the furnace perpendicular to the wall at a Arelatively low velocity. There is no high velocity air ow parallel tothe wall which would tend to interfere with burner operation if the deslagger were to be used in the burner zone. This lack of interference with the burner zone is a further advantage of my deslagger.

Although the introduction of gaseous cleaning medium between the tubes and the `slag layer is required, it is not essential that the cleaning medium be in the gaseous state initially. Water could be introduced intermediate the tubes and slag layer which would then be heated forming steam, thereby effecting the introduction of a gaseous medium intermediate the slag layer and the tubes.

While I have illustrated and described a preferred embodiment of my invention it is to be understood that such is merely illustrative and not restrictive and that variations and modifications may be made therein without departing from the spirit land scope of the invention. I therefore do not wish to be limited to the precise 5 details set forth but desire to avail myself of such changes as fall within the purview of my invention.

What I claim is:

1. In a vapor generator having a furnace, tubes lining the walls of said furnace and means vfor burning an ash bearing fuel within said furnace whereby the ash forms on the tube lined -furnace walls, an apparatus for removing ash from the furnace walls comprising: a pressure retaining chamber -outside the tubes of the tube lined furnace covering a preselected area of a furnace wall; a plurality of the tubes passing in spaced relationship across said chamber forming one side thereof, the spaces between the tubes being generally unrestricted where the tubes pass Iacross said chamber; :and means for introducing under pressure a gaseous cleaning medium into said pressure chamber and passing the cleaning medium intermediate the spaced tubes toward `the furnace, thereby removing the lash located on the area tube lined wall.

2. In ia vapor generator having a furnace of the tangent tube construction wherein tubes line the walls with small spacing between adjacent tubes, and means for burning an ash bearing fuel within said furnace whereby slag forms on the tube lined walls of said furnace, an apparatus for removing slag from the furnace wal-ls comprising: a pressure retaining chamber secured to the tubes and located on the outside of the furnace wall tubes encompassing a section of the surface of one wall of the furnace, the tubes of the tube lined furnace wall comprising one side of the pressure charnber; means for introducing a gaseous cleaning medium into said pressure chamber, the small spaces between the tagnen-t tubes being generally unrestricted where the tubes form a side of the pressure chamber whereby the gaseous cleaning medium passes intermediate the sections of furnace wall tubing associated therewith imposing a force on the slag layer generally perpendicular to the furnace wall.

3. In a vapor generator having a furnace of the web wall construction wherein tubes line :the walls with welded bars between adjacent tubes, and means for burning an ash bearing fuel within said furnace whereby slag forms on the tube lined walls of said furnace, an apparatus for removing slag from the furnace walls comprising: a pressure retaining chamber secured to the tubes and located on the outside of the furnace wall tubes, encompassing la section of the surface of one wall of the furnace, the tubes of the tube lined furnace wall comprising one side of `the pressure chamber, the bars between adjacent tubes in said section being removed throughout a major portion of' the tube length along said section, leaving a generally unrestricted opening between adjacent tubes; means for introducing a gaseous cleaning medium into said pressure chamber whereby the gaseous cleaning medium passes intermediate the sections of furnace wall tubing associated therewith imposing a force on the slag layer generally perpendicular to the furnace wall.

References Cited by the Examiner UNTTED STATES PATENTS 1,732,429 10/1929 Bell 122-390 2,028,250 1/1936 Rossner 165-95 FOREIGN PATENTS 642,575 3/ 1937 Germany. 288,830 4/1928 Great Britain.

F CHARLES I. MYHRE, Primary Examiner. 

1. IN A VAPOR GENERATOR HAVING A FURNACE, TUBES LINING THE WALLS OF SAID FURNACE AND MEANS FOR BURNING AN ASH BEARING FUEL WITHIN SAID FURNACE WHEREBY THE ASH FORMS ON THE TUBE LINED FURNACE WALLS, AN APPARATUS FOR REMOVING ASH FROM THE FURNACE WALLS COMPRISING: A PRESSURE RETAINING CHAMBER OUTSIDE THE TUBES OF THE TUBE LINED FURNACE COVERING A PRESELECTED AREA OF A FURNACE WALL; A PLURALITY OF THE TUBES PASSING IN SPACED RELATIONSHIP ACROSS SAID CHAMBER FORMING ONE SIDE THEREOF, THE SPACES BETWEEN THE TUBES BEING GENERALLY UNRESTRICTED WHERE THE TUBES PASS ACROSS SAID CHAMBER; AND MEANS FOR INTRODUCING UNDER PRESSURE A GASEOUS CLEANING MEDIUM INTO SAID PRESSURE CHAMBER AND PASSING THE CLEANING MEDIUM INTERMEDIATE THE SPACED TUBES TOWARD THE FURNACE, THEREBY REMOVING THE ASH LOCATED ON THE AREA TUBE LINED WALL. 